Combustion chamber walls and also gas turbine blades are subjected to high physical stress during operation of the gas turbine in accordance with the intended purpose. In order to make the combustion chamber and the blade more resistant to the high stress, these components are provided with cooling. If air is used as cooling medium, it is extracted from a compressor connected upstream of the combustion chamber and having a diffuser and is lost in the combustion process. Flame temperatures and NOX emissions consequently increase.
The wall of a combustion chamber is cooled in either an open or closed manner. The open cooling is in this case designed as convective cooling, film cooling or also as impingement cooling with a discharge of cooling air into the combustion space. The closed cooling requires greater design outlay and leads to an increased pressure loss on account of the cooling air conduction and the cooling itself.
In order to reduce the adverse effect caused by the extraction of cooling air, it is known to add fuel. In the prior art, this is known as cooling-air reheating or in a further sense also as progressive combustion.
To this end, U.S. Pat. No. 5,125,793 shows a turbine blade of a gas turbine having a double outer wall enclosing a cavity. A flow passage for air is arranged in the double outer wall. Flowing in the cavity is a liquid fuel which is sprayed through through-openings into the flow passage located in the double wall and which strikes a catalyst there. Due to the catalyst, the fuel decomposes endothermically into at least one combustible gas, a factor which cools the blade. The air transports the gases to an outlet, from which the mixture can flow into the turbine and burn there.
Furthermore, U.S. Pat. No. 6,192,688 discloses a combustion chamber of a gas turbine having a plurality of hollow fixed spokes, in the cavity of which a fuel is directed. The cavity is connected to the combustion space by openings. In a supply passage arranged in the outer wall of the spokes, air is additionally directed to the openings in order to obtain a combustible mixture in combination with the fuel, this combustible mixture being fed into the combustion chamber for NOx reduction during operation of the gas turbine.
In addition, U.S. Pat. No. 4,347,037 discloses a hollow turbine blade in which uniformly distributed film-cooling openings are incorporated in the side walls around which hot gas can flow. A respective outlet passage is provided for each film-cooling opening. Opening out at their inlets lying in the blade wall are in each case two separate feed passages starting at the inner cavity of the turbine blade in order to be able to direct the cooling air required for the film cooling from the cavity to the film-cooling opening.
A disadvantage with the known concepts is that, to mix cooling air and fuel, a volume has to be provided in which the reaction partners can ignite by spontaneous ignition or flashback in the components. In this way, stable combustion processes possibly form, so that the cooling effect of the fuel/air mixture is lost or the component may be damaged by the internally occurring combustion.